The uniquely facile transmission of chronic wasting disease (CWD) among cervids must underpin its uncontrolled expanding prevalence in North America, Asia and now Europe. The goal of this research is to elucidate how and why CWD is transmitted so efficiently in nature and what factors facilitate this process or influence the zoonotic risk CWD may pose. The central hypothesis for this work is that peripheral CWD prions possess characteristics that favor enhanced bioavailability, infectivity and perhaps altered zoonotic risk. CWD transmission must occur via exposure of nasal or oral mucosae to the very low concentrations of prions shed in secreta and excreta of infected cervids (6-7 log10 lower than in brain). It is likewise likely that in nature cervids are naturally exposed to excreted prions that are bound to particulates. The factors and mechanisms by which this low-level mucosal exposure initiates infection and facilitates CWD transmission remain largely mysterious and are the subject of this proposal. Amazingly, like viruses, prions can (unpredictably) evolve to cross species barriers. Humans and animals share environments and food sources contaminated with prions shed by CWD-infected cervids. The practical impact of peripheral tissue and shed prions and the role they may play in horizontal prion transmission, epidemiology, and risk posed to humans and animals remains relatively under-studied, and is the second subject of this proposal. We will address the above questions by harnessing our established robust and sensitive in vivo and in vitro prion detection methods using both native cervid and transgenic murine hosts to assess the infectivity and biochemical traits of peripheral and shed prions. These studies will be under-pinned by our unique CWD experience, facilities, and repository of tissues and excreted prions from longitudinal infection studies in deer. The study Aims are: Aim 1: To determine features of natural exposure that lead to the uniquely efficient transmission of CWD. This aim will determine if multiple low dose and/or particle binding of excreted prions enhances transmission efficiency vs. the same total encountered in a single exposure. Aim 2: To determine whether peripheral vs. brain CWD prions differ biochemically or in infectivity. We will analyze the biophysical and biochemical properties as well as cross-species infectivity and zoonotic potential of peripheral vs. CNS prions. This aim will determine whether shed CWD prions possess unique traits or broadened species barriers. The impact of this research will elucidate how and why CWD is transmitted so efficiently in nature and what factors facilitate this process or influence the zoonotic risk CWD may pose.